PROJECT SUMMARY/ABSTRACT For many autoimmune diseases new classes of biologic therapies have proven beneficial. These novel drugs that alleviate damaging inflammation were developed based on a deep understanding of the specific immune proteins (predominantly cytokines or cell membrane proteins) that cause disease pathology. To date, we lack such a sophisticated understanding of factors that cause type 1 diabetes (T1D) pathology; however, our knowledge is evolving as new discoveries shed light on mechanisms of T1D. For example, type 1 interferons (IFN1) are a family of cytokines that play a key role T1D where they impair ?-cell function, enhance immune- surveillance, and augment CD8+ cytolytic T cell (CTL) mediated ?-cell killing. IFN1 represent a key connection between immune dysregulation, ?-cell dysfunction, genes that form disease susceptibility, and environmental factors (i.e., danger signals) that collectively modulate T1D development. What is still lacking is a fundamental understanding of how IFN1 responses go awry in T1D and thus what types of interventions would be useful. This project will focus on dissecting the complex genetics of T1D to clarify mechanisms of IFN1-induced pathogenesis. At least seven T1D risk genes are involved in IFN1 production or signaling pathways (IFIH1, TYK2, SOCS1, STAT4, PTPN2, PTPN22, and IL10). Two of these genes, IFIH1 and TYK2, have coding variants that are associated with T1D risk. Hence, these genes are excellent targets for genotype:phenotype studies. IFN-induced with helicase C domain 1 (IFIH1) is a cytoplasmic protein that binds to viral RNA structures upon infection, triggering downstream signaling to elicit IFN1 production. How IFIH1 coding variants affect responses by ?-cells or immune cells (with Project 2) to self- or viral-RNA molecules will be the focus of Aim 1. Previous studies have identified a P1104A coding variant in TYK2 as associated with protection against T1D. Like IFIH1 variants, this TYK2 allotype alters IFN1 signaling in immune cells and could impact IFN1 signaling in islet cells. How the TYK2 variant affects ?-cell (with Project 2) or immune cell responses (with Project 3) to IFN1 will be the focus of Aim 2. We predict that IFIH1 risk variants are excessively sensitive to self-RNA species or short viral dsRNA. We also predict that TYK2 risk variants allow maximal IFN1 induced signaling leading to IFN-induced ?-cell failure or IFN-induced CTL effector function. We hypothesize that risk alleles of IFIH1 and TYK2 improperly integrate responses to cellular danger signals, leading to immune dysregulation and T1D onset. This project will utilize an extensive repository of deeply genotyped T1D and control donor cells as well as induced pluripotent stem cells (iPSCs), to interrogate precise questions surrounding how mechanisms of innate immune sensing and IFN1 production lead to ?-cell loss in T1D. These studies are highly synergistic with Projects 2 & 3 are will rely heavily of Cores A & B for successful completion.